THE MEAN WORK FUNCTION EFFECTIVE FOR POSITIVE ION EMISSION FROM POLY- AND MONOCRYSTALLINE SURFACES

2005 ◽  
Vol 12 (01) ◽  
pp. 107-113 ◽  
Author(s):  
HIROYUKI KAWANO
Keyword(s):  
Work Function ◽  
Electron Emission ◽  
Heterogeneous Surfaces ◽  
Polycrystalline Metals ◽  
Typical Data ◽  
The Mean ◽  
Ion Emission ◽  
Thermionic Property ◽  
Positive Ion ◽  
Good Agreement

To clarify the thermionic property of solids, the mean work function effective for positive ion from polycrystalline surfaces (ϕ+) is theoretically studied together with that for electron emission (ϕe). The theoretical values of ϕ+ and ϕe thus evaluated typically with W are in good agreement respectively with those experimental ones accepted today. The thermionic contrast (Δϕ* ≡ ϕ+ – ϕe) is determined to be 0.56–0.57eV for W. For other polycrystalline metals (Nb, Mo, Ta, Re, Ir and Pt), it ranges from about 0.4 to 0.8eV in contrast with monocrystalline ones having Δϕ* = 0. Consequently, the fact of Δϕ* > 0 should be taken into consideration with any polycrystalline surface, and ϕ+ should be adopted whenever we try to analyze those data on positive ion emission due to any of the processes such as thermal stimulation and ion bombardment at heterogeneous surfaces. This article concludes that such typical data on thermal- and secondary-positive ion emissions are analyzed reasonably by adoption of ϕ+ instead of ϕe.

scholarly journals The temperature variation of the work function of clean and of thoriated tungsten

1937 ◽  
Vol 163 (915) ◽  
pp. 499-510 ◽  
Keyword(s):  
Work Function ◽  
Temperature Variation ◽  
Transmission Coefficient ◽  
Electron Emission ◽  
Universal Constant ◽  
Absolute Temperature ◽  
Theoretical Equation ◽  
Restricted Range ◽  
Thoriated Tungsten ◽  
The Mean

It is well known that the relation between the electron emission i from a hot body and its absolute temperature T may be expressed empirically by the equation i = AT 2 e -ψ/ kT , in which A and ψ are constants characteristic of the emitting surface, and k is Boltzmann’s constant. This is of the same form as the theoretical equation i = A 0 D - T 2 e -x/ kT , in which A 0 is a universal constant having the numerical value of 120 amp. cm. -2 degree -2 , D - is the mean transmission coefficient, and X is the work function of the emitter. This quantity is not necessarily constant with temperature, and if we assume its temperature variation to be linear, as we may do within a sufficiently restricted range of temperatures, setting X = ω+α KT , Where ω and α are Constants, we may rewrite(2) thus: i = A 0 D - T 2 e -ω/ kT . It may be shown (cf. Reimann 1934a, p. 265) that in such cases as occur in nature D - probably never varies appreciably with temperature, and so, assuming this, and comparing (1) with (4), we may write A = A 0 D - e-α, ψ = ψ .

scholarly journals Thermionic effects caused by vapours of alkali metals

1925 ◽  
Vol 107 (741) ◽  
pp. 61-79 ◽  
Keyword(s):  
Work Function ◽  
Electron Affinity ◽  
Alkali Metals ◽  
Tungsten Filament ◽  
Square Roots ◽  
Thoriated Tungsten ◽  
Current Flows ◽  
The Masses ◽  
Ion Emission ◽  
Positive Ion

Early in 1923 it was shown that a tungsten filament heated to 1200° K or more in saturated cæsium vapour converts all cæsium atoms which strike it into cæsium ions. Thus when the filament is surrounded by a negatively charged cylinder a positive ion current flows from the filament, which is independent of the filament temperature (above 1200° K) and independent of the applied potential, if this is sufficient to overcome the space charge effect of the positive ions. At lower voltages the currents follow the 3/2 power law, and the currents are smaller than the corresponding electron currents obtainable from the same filament in the ratio of the square roots of the masses of the electrons and cæsium ions. The reason that the cæsium atoms lose their valence electrons so readily upon contact with the filament, is merely that the electron affinity of tungsten (Richardson work function) is 4·53 volts, while the electron affinity of a cæsium atom (ionising potential) is only 3·88 volts. Experiments showed in fact that if the work function for the filament is lowered to 2·69, by allowing a monatomic layer of thorium atoms to accumulate on the surface (by diffusion from the interior of a thoriated tungsten filament), the positive ion emission becomes negligible.

Simultaneous Determination of Alogliptin, Linagliptin, Saxagliptin, and Sitagliptin in Bulk Drug and Formulation by UPLC Q-TOF-MS

2020 ◽  
Vol 17 (1) ◽  
pp. 95-105
Author(s):  
Ramji Rathod ◽  
Faraat Ali ◽  
Amrish Chandra ◽  
Robin Kumar ◽  
Meenakshi Dahiya ◽  
...  
Keyword(s):  
Internal Standard ◽  
Gradient Elution ◽  
Ultra Performance Liquid Chromatography ◽  
Pharmaceutical Dosage Forms ◽  
Sensitivity And Selectivity ◽  
The Mean ◽  
Bulk Drug ◽  
Positive Ion ◽  
Higher Sensitivity

Background: A simple and sensitive Ultra Performance Liquid Chromatography-Mass Spectrometry method was developed and validated to measure the concentrations of Alogliptin (ALO), Linagliptin (LIN), Saxagliptin (SAX), and Sitagliptin (SIT) using Pioglitazone (PIO) as an internal standard. Methods: Chromatographic separation of six gliptins was achieved on a C-18 column (100×2.1 mm, 2.7 μm) using a mobile phase consisting of formic acid in water, 0.1%v/v: acetonitrile in gradient elution. Electrospray ionization (ESI) source was operated in the positive ion mode. Targeted MS/MS mode on a QTOF MS was used to quantify the drug utilizing the transitions of 340.1(m/z), 473.2 (m/z), 316.2 (m/z), 408.1 (m/z), and 357.1 (m/z) for ALO, LIN, SAX, SIT and PIO respectively. Results: As per ICH Q2R1 guidelines, a detailed validation of the method was carried out and the standard curves were found to be linear over the concentration ranges of 1516.0-4548.1 ng mL-1, 519.8- 1559.4 ng mL-1, 1531.4-4594.3 ng mL-1and 1519.6-4558.8 ng mL-1 for ALO, LIN, SAX and SIT respectively. Precision and accuracy results were within the acceptable limits. The mean recovery was found to be 98.8 _ 0.76 % (GEM), 102.2 _ 1.59 % (LIN), 95.3 _ 2.74 % (SAX) and 99.2 _ 1.75 % (SIT) respectively. Conclusions: The optimized validated UPLC QTOF-MS/MS method offered the advantage of shorter analytical times and higher sensitivity and selectivity. The optimized method is suitable for application in quantitative analysis of pharmaceutical dosage forms for QC laboratory.

Computational Investigation of Different Turbulent Models When Predicting Airflow in an Enclosure

2008 ◽  
Author(s):  
Xi Wang ◽  
Hassan Naji ◽  
Ahmed Mezrhab
Keyword(s):  
Numerical Investigation ◽  
Turbulence Models ◽  
Turbulent Stress ◽  
Computational Investigation ◽  
Isothermal Case ◽  
The Mean ◽  
Turbulent Models ◽  
Rsm Model ◽  
Cold Case ◽  
Good Agreement

In the present study, a numerical investigation is carried out for an isothermal case, a hot case and a cold case with FLUENT code. Three turbulence models are considered: the k-ε realisable model, the RNG k-ε model and the RSM linear model. The obtained results are compared to experiments and show generally a good agreement for the mean velocities and temperatures, but less satisfactory for the turbulent stress. The performance of the RSM model is remarkable. Even if none of the models is able to give the exact experimental pattern on the map of turbulence, the RSM model seems able to predict such configuration.

EFFECT OF GRAIN SIZE ON THE ELECTRON WORK FUNCTION OF Cu AND Al

2004 ◽  
Vol 11 (02) ◽  
pp. 173-178 ◽  
Author(s):  
WEN LI ◽  
D. Y. LI
Keyword(s):  
Grain Size ◽  
Phase Transformation ◽  
Grain Boundary ◽  
Work Function ◽  
Electron Work Function ◽  
Deformation Texture ◽  
Kelvin Probe ◽  
Surface Conditions ◽  
The Mean ◽  
Sophisticated Instrument

The Kelvin probe is a sophisticated instrument which is very sensitive to changes in surface conditions, such as deformation, texture, phase transformation and contamination. Efforts have been made to use this technique to diagnose wear. In this study, the effect of the grain boundary (GB) on the electron work function (EWF) was examined with the aim of investigating the contribution of changes in grain size to total changes in the EWF during wear. Copper and aluminum were studied as examples. It was demonstrated that the EWF dropped in the vicinity of GB's and the mean EWF decreased as the grain size decreased. The mechanism responsible for the changes in the EWF with respect to the GB is discussed.

Respiratory Exchange and Body Size in the Aldabra Giant Tortoise

1971 ◽  
Vol 55 (3) ◽  
pp. 651-665 ◽  
Author(s):  
G. M. HUGHES ◽  
R. GAYMER ◽  
MARGARET MOORE ◽  
A. J. WOAKES
Keyword(s):  
Body Weight ◽  
Body Size ◽  
Metabolic Rate ◽  
Relative Proportion ◽  
The Body ◽  
O2 Consumption ◽  
Weight Range ◽  
Testudo Hermanni ◽  
The Mean ◽  
Good Agreement

1. The O2 consumption and CO2 release of nine giant tortoises Testudo gigantea (weight range 118 g-35·5 kg) were measured at a temperature of about 25·5°C. Four European tortoises Testudo hermanni (weight range 640 g-2·16 kg) were also used. The mean RQ values obtained were 1·01 for T. gigantea and 0·97 for T. hermanni. These values were not influenced by activity or size. 2. The data was analysed by plotting log/log regression lines relating body weight to O2 consumption. Both maximum and minimum metabolic rates recorded for each individual T. gigantea showed a negative correlation with body weight. For active rates the relation was O2 consumption = 140·8W0·97, whereas for inactive animals O2 consumption = 45·47W0·82. 3. The maximum rates were obtained from animals that were observed to be active in the respirometer and the minimum rates from animals that remained quiet throughout. The scope for activity increased with body size, being 82 ml/kg/h for animals of 100 g and 103 ml/kg/h for 100 kg animals. The corresponding ratio between maximum and minimum rates increases from about 2 to 6 for the same weight range. 4. Values for metabolic rate in T. hermanni seem to be rather lower than in T. gigantea. Analysis of the relative proportion of the shell and other organs indicates that the shell forms about 31% of the body weight in adult T. hermanni but only about 18% in T. gigantea of similar size. The shell is not appreciably heavier in adult T. gigantea (about 20%). 5. Data obtained for inactive animals is in good agreement with results of other workers using lizards and snakes. Previous evidence suggesting that chelonians show no reduction in metabolic rate with increasing size is not considered to conflict with data obtained in the present work.

Correlation between the sea level muon spectrum and the primary nucleon spectrum using the Cocconi–Koester–Perkins model

1979 ◽  
Vol 57 (7) ◽  
pp. 921-925 ◽  
Author(s):  
A. K. Chakrabarti ◽  
A. K. Das ◽  
A. K. De
Keyword(s):  
Sea Level ◽  
Pion Production ◽  
Spectral Shape ◽  
Muon Spectrum ◽  
Proton Proton ◽  
Absolute Value ◽  
Nucleon Spectrum ◽  
Scaling Models ◽  
The Mean ◽  
Good Agreement

Using the recent ISR data of proton–proton interactions on the inclusive production of pions and nucleons, realistic values of the mean pion inelasticity Kπ and the mean nucleon inelasticity KT have been estimated. These values have been used for the derivation of the sea level differential muon spectrum from the primary nucleon spectrum and vice versa using the CKP model as an extension of the work presented in an earlier article. It is found that none of the measured primary nucleon spectra of Ryan, Ormes, and Balasubrahmanyan and Grigorov, Rapoport, and Shestoperov fit any of the precisely measured muon spectra of Ayre, Baxendale, Hume, Nandi, Thompson, and Whalley and Allkofer, Carstensen, and Dau in spectral shape or the absolute value. On the other hand good agreement between the derived muon spectra and the spectra of Allkofer et al. and Ayre et al. is found if the primary nucleon spectra of the forms, N(Ep) = (1.38 ± 0.08)Ep−2.59 and N(Ep) = (1.00 ± 0.10)Ep−2.55, respectively, are assumed. The first form is comparable with that obtained by Brooke, Hayman, Kamiya, and Wolfendale following more approximate but similar procedure. It is also not unjustified when compared with the measured primary all nuclei spectrum of Grigorov et al. in the light of suggestions made by Ellsworth, Ito, Macfall, Siohan, Streitmatter, Tonwar, Vishwanath, Yodh, and Balasubrahmanyan. By comparing the pion production spectra derived from the same primary nucleon spectrum but using the CKP and the scaling models, it is concluded that the results are sensitive to the model assumed for the collisions.

Drei Verfahren zur Messung der Änderung der Austrittsarbeit mit Hilfe der Oberflächenionisation

1972 ◽  
Vol 27 (5) ◽  
pp. 794-803 ◽  
Author(s):  
R Müller ◽  
W Walcher ◽  
H.-W Wassmuth
Keyword(s):  
Work Function ◽  
Mass Spectrometer ◽  
Reference Electrode ◽  
Surface Ionization ◽  
Contact Potential ◽  
External Voltage ◽  
The Third ◽  
Metal Atoms ◽  
Ion Emission

AbstractThree methods for the measurement of the change ΔΦ of the work function Φ of a metal surface due to the presence of adsorbed particles (e. g. oxygen) have been developed utilizing the surface ionization of a beam of metal atoms (e. g. In, Sr) as a probe. The experiments have been performed with a mass spectrometer at ultrahigh vacuum.In the first method the temperature dependency of the ion emission current is used for the determination of the work function Φ considering certain limiting conditions. The two other methods which may be applied simultaneously with the first one, involve a direct measurement of ΔΦ by compensating the change of the contact potential by an external voltage: In the second method the contact potential between the ionizing surface and a surrounding reference electrode is used to control the ion optical conditions for the ion emission, whereas in the third method the change in the kinetic energy of the ions caused by a change of the contact potential between the ionizing surface and the entrance slit of the mass spectrometer is used as a measure of ΔΦ

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